MATH - solving exponential equations

posted by .

The half-life of sodium-24 is 14.9 hours. A hospital buys a 40 mg sample of sodium-24.
a) How many grams, to the nearest tenth, of sodium-21 will remain after 48 h?
b) After how long will only 2.5 mg remain?

I don't know how to write the exponential function in order to be able to solve this. ><

  • MATH - solving exponential equations -

    amount = 40(1/2)^(t/14.9) , where t is the number of hours.

    test: if t = 0, Amount = 40 , Check!
    if t = 14.9
    amount = 40(1/2)^1 = 20 , Check!


    a) if t = 48
    Amount = 40(1/2)^(48/14.9)
    = 40(1/2)^3.22147651
    = 40(.107210899)
    = appr. 4.29 g

    b) 2.5 = 40(1/2)^(t/14.9)
    .0625 = (.5)^(t/14.9)
    t/14.9 = ln.0625/ln.5
    t/14.9 = 4
    t = 4(14.9) = 59.6 hours

Respond to this Question

First Name
School Subject
Your Answer

Similar Questions

  1. Chemistry

    Which radioactive sample would contain the greatest remaining mass of the radioactive isotope after 10 years?
  2. math

    One-half serving of soy sauce contains 389 milligrams of sodium. How many grams of sodium from soy sauce are included in an egg-foo-young dish made from 4 servings of soy sauce?
  3. Chem

    What percentage of sodium-24 with a half life of 15.0 hr would remain after 60hours?
  4. Chemistry

    A sample of sodium-24 with an activity of 12 mCi is used to study the rate of blow flow in the circulatory system. If sodium -24 has a half-life of 15 hours, what is the activity of the sodium after 2.5 d ?
  5. chemistry

    The data in the table show the amount of a 500 g sample of sodium-24 over time. Make a graph of the data (remember to label all axes and title the graph). What is the half-life of sodium-24?
  6. math grade 12

    2. An isotope of sodium has a half-life of 15 h. A sample of this isotope has a mass of 2 g. a. [2] Find the mass equation that remains after t hours. b. [1] Find the mass that remains after 5 hours, to the nearest hundredth. c. [2] …
  7. chemistry

    a sample of sodium-24 with an activity of 12 mCi is used to study the rate of blood flow in the circulatory system. If sodium-24 has a half-life of 15 h, what is the activity of the sodium after 2.5 days. please show work.
  8. physical science

    sodium-24 has a half life of 15 hours,how much of a 50 gram sample will be left after 60 hours
  9. chemistry

    2.The data in the table show the amount of a 500 g sample of sodium-24 over time. Make a graph of the data (remember to label all axes and title the graph). What is the half-life of sodium-24?
  10. math

    The radioactive isotope sodium-24 is used as a tracer to measure the rate of flow in an artery or vein. The half life of sodium-24 is 14.9 hours.Suppose that a hospital buys a sample of sodium-24 a. how much of the sample will remain …

More Similar Questions